Conventional bolts are formed from rod stock by a process called cold heading, upset forging or pressing. A die impacts an elongated rod to compress the stock axially, thereby forcing the stock material to flow radially outwardly within the limits of the die cavity; the deformed material forms the head of the bolt. Hot pressing is advantageous in that the heated stock is more easily deformed by the die or punch. However, hot pressing requires wider tolerances because of shrinkage variations; also the tooling is more expensive and elaborate. Cold heading is a relatively simple process, but sometimes requires a two stage progressive die system wherein the head material is subjected to two or more successive deformations by differently configured die members.
The present invention relates to a bolt that can be formed by the cold heading process with only one deforming operation on the head material proper. A principal aim of the invention is to reduce the energy costs associated with operating the die system. A secondary aim is to produce a bolt having an inherently stronger design that is relatively free from internal stresses, particularly certain stress-riser conditions that can exist at the joint between the head and shank portions of conventionally-formed bolts.
The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without payment to me of any royalty thereon.